#include <stdio.h>
#include <math.h>

int main()
{
    float x1,y1,x2,y2;
    while(scanf("%f %f %f %f",&x1,&y1,&x2,&y2)!=EOF)
    {
    	printf("%.2f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
    }
    return 0;
}